Montelukast's Side Effects
For Parents
For Health Care Professionals
Links and Resources

Side effects from montelukast can happen at any time during treatment:

Parents have reported to Parents United for Pharmaceutical Safety and Accountability that their children began experiencing side effects days, weeks, months, and even years after treatment with montelukast began. Some parents reported they observed side effects only after a dosage increase. Parents have also reported that side effects worsened, and/or new side effects happened after a dosage increase. Some reported side effects only after stopping and restarting the medication.

A comprehensive list of Montelukast's side effects is available here and include the following psychiatric disorders (this information is current as of February 2019):

agitation, aggressive behavior or hostility, anxiousness, depression, disorientation (confusion), disturbance in attention, dream abnormalities (bad/vivid dreams), dysphemia (stuttering), hallucinations, insomnia (trouble sleeping), irritability, memory impairment, obsessive-compulsive symptoms, restlessness, somnambulism (sleep walking), suicidal thinking and behavior (including suicide), tic, and tremor.

In addition, patients with asthma on therapy with montelukast sodium may present with systemic eosinophilia, sometimes presenting with clinical features of vasculitis consistent with Churg-Strauss syndrome, a condition which is often treated with systemic corticosteroid therapy. These events have been sometimes associated with the reduction of oral corticosteroid therapy. Physicians should be alert to eosinophilia, vasculitic rash, worsening pulmonary symptoms, cardiac complications, and/or neuropathy presenting in their patients. A causal association between montelukast sodium and these underlying conditions has not been established.


ASTHMA was reported as a "drug related adverse experience" in children ages 6 months to 2 years of age in a clinical study of 175 pediatric patients. Canadian "Product Monograph".


According to the Canadian Product Monograph, in a clinical study of 175 pediatric patients 6 months to 2 years of age, HYPERKINESIA was reported as a drug related adverse experience in >1% of patients treated with montelukast and at a greater incidence than in patients treated with placebo. 

Hyperkinesia is a movement disorder characterized by excessive spontaneous movement or abnormal involuntary movement.

A search for "hyperkinesia" on the US National Library of Medicine's MedlinePlus website gives the reader information on ATTENTION DEFICIT HYPERACTIVITY DISORDER.

Children taking Montelukast have been diagnosed with ADHD.****

According to Public Citizen's WorstPills.org website, montelukast can cause blood vessel inflammation, liver disease, lupus, and recurrences of ulcerative colitis.


Psychiatric disorders can be disabling and more than 90% of all suicides are related to a mood disorder or other psychiatric illness*.


An unpleasant state of extreme arousal, increased tension (anxiety, stress, jitters), and irritability. Extreme agitation can lead to confusion, hostility, and hyperactivity.*

Child may have difficulty concentrating or making decisions, be easily distracted, have difficulty sitting still or controlling impulses, and may engage in aggressive behavior.

Example: Child may have difficulty participating in quiet activities (such as reading); may fidget, move constantly, or wander; may talk too much, antagonize peers or instigate fights.


Aggression is described as hostile (antagoinnistic, unfriendly, hateful) or destructive behavior or actions** and can involve:

- unprovoked violent action 
- deliberately unfriendly behavior
- physical or verbal behavior that is intended to cause pain or harm to another.

Example: Child may be oppositional, defiant, combative, quarrelsome; may threaten harm to others; may engage in purposeful and unprovoked attacks on others.


Anxiety is a feeling of apprehension or fear.

Anxiety is often accompanied by physical symptoms, including:
twitching, trembling or tremor; muscle tension; headaches; sweating; dry mouth; difficulty swallowing; abdominal pain (may be the only symptom, especially in a child)

Sometimes other symptoms accompany anxiety:
dizziness; rapid or irregular heart rate; rapid breathing; diarrhea or frequent need to urinate; fatigue; irritability, including loss of temper; sleeping difficulties and nightmares; decreased concentration; sexual problems (in adults) *

Children may express anxiety in the following ways:

-excessive worry (child shows age inappropriate separation anxiety, child worries constantly that parents are going to die)

-abnormal fear of leaving the home (child predictably shows resistance or throws tantrums whenever it is time to go somewhere)

-obsessive compulsive behavior: persistent, irrational, uncontrollable thoughts/behaviors (constantly talking about a particular subject to the extent that it interferes with normal communication, worrying about germs, repeated hand washing or checking things)

-phobias: irrational and disruptive fears of specific objects or social situations


In addition to nightmares, parents have reported night terrors: a sleep disorder in which a person quickly awakens from sleep in a terrified state.

Also called pavor nocturnus or sleep terrors, they occur during deep sleep and usually happen in the first half of the night. The child often screams, and will usually not remember the details of the scare. You may be unable to talk to a child who is having a night terror. In contrast, nightmares are normal on occasion, especially after someone watches frightening movies/TV shows or has an emotional experience. A person may remember the details of a dream upon awakening, and will not be disoriented after the episode.*

In research conducted by Rebecca Bernert, a doctoral candidate in clinical psychology at Florida State University who specializes in the relationship between sleep and suicidal thoughts and behaviors, the presence of severe and frequent nightmares or insomnia was a strong predictor of suicidal thoughts and behaviors. Other studies have established a link between chronic sleep disruption and suicide.

Sleep complaints, which include nightmares, insomnia and other sleep disturbances, are listed in the current Substance Abuse and Mental Health Services Administration's inventory of suicide-prevention warning signs.


In clinical trials, depression was reported in children taking montelukast and in adults taking montelukast and placebo. In one adult in the montelukast group, depression was considered drug related by the investigator.

FDA Medical Review for Singulair5 MG (page 21)
FDA Medical Review for Singulair10 MG (pages 78-80)

Depression may be described as feeling sad, blue, unhappy, miserable, or down in the dumps. Most of us feel this way at one time or another for short periods.

Clinical depression is a mood disorder in which feelings of sadness, loss, anger, or frustration interfere with everyday life for an extended period of time. Symptoms include:

-trouble sleeping or excessive sleeping
-dramatic change in appetite, often with weight gain or loss
-fatigue and lack of energy
-feelings of worthlessness, self-hate, and inappropriate guilt (low self esteem)
-extreme difficulty concentrating
-agitation, restlessness, and irritability (and sudden bursts of anger)
-inactivity and withdrawal from usual activities
-feelings of hopelessness and helplessness
-recurring thoughts of death or suicide

Depressed children may not have the classic symptoms of adult depression. Watch especially for changes in school performance, sleep, and behavior.*

Mood disorders are characterized by inappropriate, exaggerated, or limited range of feelings. To be diagnosed with a mood disorder, feelings must be to the extreme.  In other words, crying, and/or feeling depressed, suicidal frequently. Or, the opposite extreme, having excessive energy where sleep is not needed for days at a time and during this time the decision making process is significantly hindered. Bipolar disorder (which has also been reported as an adverse reaction to Singulair) is also a mood disorder.***




Hallucinations involve sensing (seeing, hearing, feeling, smelling, or tasting) things that aren't there while a person is awake and conscious.*****


Seeing patterns, lights, beings, or objects that aren't there
Hearing voices when no one has spoken
Feeling a crawling sensation on the skin


Insomnia is defined by the National Institutes of Health* as:
"a hard time falling or staying asleep."

According to the FDA's Updated Information on Leukotriene Inhibitors: Montelukast (marketed as Singulair), Zafirlukast (marketed as Accolate), and Zileuton (marketed as Zyflo and Zyflo CR), in clinical trials, sleep disorders  (primarily insomnia) were reported more frequently with all three products compared to placebo.

In research conducted by Rebecca Bernert, a doctoral candidate in clinical psychology at Florida State University who specializes in the relationship between sleep and suicidal thoughts and behaviors, the presence of severe and frequent nightmares or insomnia was a strong predictor of suicidal thoughts and behaviors. Other studies have established a link between chronic sleep disruption and suicide. 

Sleep complaints, which include nightmares, insomnia and other sleep disturbances, are listed in the current Substance Abuse and Mental Health Services Administration's inventory of suicide-prevention warning signs.


The state of being easily irritated or annoyed; readily excited to impatience or anger; abnormally sensitive to a stimulus. Younger children may be fussy or whiny; older children may get extremely angry over imagined slights or minor disagreements/issues; child may be oversensitive to or intolerant of loud noises, bright lights, or physical sensations. 

A parent reported that a medical professional recommended her child be evaluated for Asperger syndrome (an autistic spectrum disorder) when she reported that her child was hypersensitive to tags in his clothes, seams in his socks, and his clothes and shoes always felt "too tight". This behavior stopped after the child stopped taking montelukast.


Another term for agitation.


Somnambulism (sleepwalking) is a sleep disorder that falls under the parasomnia group. Parasomnias are undesirable motor, verbal, or experiential events that occur during sleep. Night terrors/sleep terrors are also in this group.***


Suicide is the act of deliberately taking one's own life. Suicidal behavior is any deliberate action with potentially life-threatening consequences, such as taking a drug overdose or deliberately crashing a car. Suicidal behaviors can accompany many emotional disturbances, including depression...More than 90% of all suicides are related to a mood disorder or other psychiatric illness.*

Early signs:

- depression
- statements or expressions of guilt
- tension or anxiety
- nervousness
- impulsiveness

Critical signs:

- sudden change in behavior, especially calmness after a period of anxiety
- giving away belongings/attempts to "get one's affairs in order"
- direct or indirect threats to commit suicide
- direct attempts to commit suicide

Suicide attempts and threats should always be taken seriously. About one-third of people who attempt suicide will repeat the attempt within 1 year, and about 10% of those who threaten or attempt suicide eventually do kill themselves.*


A tic is a sudden, repetitive movement or sound that can be difficult to control. Tics involving movements are called motor tics. Tics involving sounds are called vocal tics. Tics can be either simple or complex. Simple motor tics involve a single muscle group. Complex motor tics usually involve more than one muscle group.*


Involuntary (not on purpose) shaking of the body or limbs. 

Tremors may affect the hands, arms, head, eyelids, voice box, or other muscles. They rarely affect the legs or feet.

The shaking usually involves small, rapid movements -- more than 5 times a second.

The tremors may: occur when you move (action-related tremor), and may be less noticeable with rest; come and go; disappear with sleep; get worse with stress, caffeine, and certain medications; not affect both sides of the body the same way.

Head nodding may be a symptom of a tremor.

If the tremor affects the voice box, the voice may have a shaking or quivering sound.*

EOSINOPHILIA is an increased number of eosinophils. Eosinophils are a type of white blood cell, which contain particles filled with chemicals that fight off infections and are one of the types of cells involved in allergic reactions. Eosinophils are found in small numbers in the blood and small intestine. The body may produce more of them in response to allergic disorders, inflammation of the skin, and parasitic infections. If eosinophils move outside the bloodstream/intestines into organs and tissues, they can cause inflammation and damage.*****

For example, if eosinophils invade the esophagus, the following symptoms may occur: nausea, regurgitation, vomiting, abdominal pain, a burning feeling similar to acid reflux (heartburn) that does not respond to antacids, difficulty swallowing and gagging, feeling like something is stuck in the throat. Children may be reluctant to eat and develop irrational aversions to certain foods.

VASCULITIS is an inflammation of the blood vessels. In vasculitis, the body’s immune system mistakenly attacks the body’s own blood vessels, causing inflammation that can damage the blood vessels and lead to a number of serious complications.

Vasculitis is sometimes a side effect of the body's response to an infection or an allergic reaction to a medication. 

Symptoms may include include general aches, pains, and sickness, such as fever, loss of appetite, weight loss, fatigue (feeling tired) and weakness.

Other symptoms may be specific to certain body systems or organs:

Skin: a variety of skin changes, including purple or red spots. The changes may look like clusters of small dots, splotches, bruises, or hives. They may be itchy or painless.
Joints: aches and arthritis if the joints are affected.

Lungs: may experience shortness of breath or even cough up blood. On a chest x-ray, lung symptoms may look like pneumonia, even though they are not.

Gastrointestinal tract: may include ulcers in the mouth, abdominal pain or bloody diarrhea

Sinuses, nose, and ears: sinus infections, chronic middle ear infections, ulcers in the nose, hearing loss.

Eyes: blurring or loss of vision.

Brain: headaches, confusion, changes in behavior, or strokes.

Nerves: numbness, tingling, and weakness in various parts of the body; loss of feeling or strength in the hands and feet or shooting pains in the arms and legs.*****

CHURG-STRAUSS SYNDROME is a type of vasculitis. It can affect many different organs, but it most commonly affects the lungs, skin, kidneys, and heart. Many people who are diagnosed with Churg-Strauss syndrome also have asthma. They may have had preexisting, newly diagnosed, or recently worsened asthma when diagnosed with Churg-Strauss syndrome.******

Churg-Strauss Syndrome is also called Allergic granulomatosis angiitis.

CSS can also involve the central nervous system, peripheral nervous system, gastrointestinal system, musculoskeletal system, and the optic nerve.

Refer to the "Links and Resources" page for more information.



ASTHMA symptoms in children with no history of asthma who were prescribed montelukast for allergies

Resolution of asthma symptoms when montelukast was discontinued

frequent urination/daytime wetting accidents

daytime soiling accidents (encopresis)

cold sores

hair loss

bleeding ears

difficulty swallowing/lump in throat

sensation of choking

fear of eating/choking

bipolar disorder

depression requiring hospitalization

trichotillomania (pulling out one's own scalp or body hair)


severe nail biting

bruxism (teeth grinding)

excessive sweating

excessive thirst

excessive hunger

appetite loss

weight gain

weight loss

dilated pupils

intestinal ulcers

stomach ulcers


Some over the counter medicines also have psychiatric or behavioral side effects, which may not be listed on product packaging or product websites. 

One source of information is WebMD Drugs & Medications A-Z. Click on the "Does [name of drug] have any side effects?" box after clicking on the "Side Effects" tab.

FDA MedWatch Adverse Event Reporting System

*MedLine Plus Medical Encyclopedia, a service of the US National Library of Medicine and the National Institutes of Health

**The American Heritage® Dictionary of the English Language, Fourth Edition. Retrieved September 24, 2008, from Dictionary.com

***Diagnostic and Statistical Manual of Mental Disorders Fourth Edition, presented by
AllPsych ONLINE, one of the largest and most comprehensive psychology websites on the Internet. The DSM-IV is published by the American Psychiatric Association and covers all mental health disorders for both children and adults. It is the standard classification of mental disorders used by mental health professionals in the United States.

****This information is based on parent reports submitted to or reviewed by Parents United for Pharmaceutical Safety and Accountability advocates.

*****From MedlinePlus, a service of the US National Library of Medicine and the National Institutes of Health:

******From the National Heart Blood and Lung Institute website:


Disclaimer: Parents United for Pharmaceutical Safety and Accountability is a volunteer patient advocacy group. Consult a licensed health care professional before making any medical decisions. Do not stop administering an asthmatic child's medications without the supervision of the child's healthcare provider. The information on this site is intended for educational purposes and should not be construed as medical advice. It is accurate to the best of our knowledge. If you discover an inconsistency, please bring it to our attention.